MLA
Moses, L. Z. Letter from L. Z. Moses (Centreville, Virginia), to "Dear Father, Mother, Brothers and Sisters," Regarding the Battle of Dranesville - December 21, 1861. 1861. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 5, Folder 33. https://digital.library.emory.edu/purl/822h70rzxx-cor.
APA, 6th edition
Moses, L. Z. (1861). Letter from L. Z. Moses (Centreville, Virginia), to "Dear father, mother, brothers and sisters," regarding the battle of Dranesville - December 21, 1861 (Box 5, Folder 33) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/822h70rzxx-cor.
Chicago
Moses, L. Z. “Letter from L. Z. Moses (Centreville, Virginia), to ‘Dear Father, Mother, Brothers and Sisters," Regarding the Battle of Dranesville - December 21, 1861.” Letters (correspondence). Civil War Collection, 1861. Box 5, Folder 33. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/822h70rzxx-cor.